1. Field of the Invention
The present invention relates to piezoelectric ceramic compositions and piezoelectric ceramic devices using the compositions. Particularly, the present invention relates to piezoelectric ceramic compositions which are useful as, for example, materials for piezoelectric ceramic filters, piezoelectric ceramic oscillators, piezoelectric ceramic resonators and other piezoelectric ceramic devices, and piezoelectric ceramic devices using the compositions.
2. Description of the Related Art
Piezoelectric ceramic compositions mainly containing lead titanate zirconate (Pb(TixZr1xe2x88x92x)O3) or lead titanate (PbTiO3) have been widely used as piezoelectric ceramic compositions for piezoelectric ceramic filters, piezoelectric ceramic oscillators, piezoelectric ceramic resonators and other piezoelectric ceramic devices. Such piezoelectric ceramic compositions mainly containing lead titanate zirconate or lead titanate inevitably contain large amounts of lead as a component, and lead oxide vaporizes during production to deteriorate the uniformity of characteristics of the produced devices. To avoid deteriorated uniformity of characteristics of the produced devices due to vaporization of lead oxide in the production step, piezoelectric ceramic compositions containing no or small amounts of lead are preferred.
In contrast, piezoelectric ceramic compositions mainly containing SrBi2Nb2O9 or other layered bismuth compounds include no lead oxides in the composition and do not invite the above problem. However, when piezoelectric ceramic filters or oscillators are prepared using such piezoelectric ceramic compositions mainly containing SrBi2Nb2O9 or other layered bismuth compounds, the resulting piezoelectric ceramic filters or oscillators exhibit greater temperature-dependent factors of resonant frequency than conventional compositions containing lead zirconate titanate or lead titanate, and have not yet been in wide practical use.
Accordingly, it is a main object of the invention to provide piezoelectric ceramic compositions mainly containing SrBi2Nb2O9 which have improved temperature-dependent factors of resonant frequency frTc shown by the following equation
frTC=(fr(max)xe2x88x92fr(min))/(fr(20xc2x0 C.)xc3x97100)
wherein fr(max) is the maximum resonant frequency within the range from xe2x88x9220xc2x0 C. to 80xc2x0 C.; fr(min) is the minimum resonant frequency within the range fromxe2x88x9220xc2x0 C. to 80xc2x0 C.; and fr(20xc2x0 C.) is the resonant frequency at 20xc2x0 C. within a temperature range fromxe2x88x9220xc2x0 C. to 80xc2x0 C., and are useful as materials for piezoelectric ceramic devices, especially for piezoelectric ceramic oscillators, and to provide piezoelectric ceramic devices using the compositions.
The invention provides, in an aspect, a piezoelectric ceramic composition mainly contains a component shown by the formula SrBi2Nb2O9 and includes at least a trivalent metallic element other than the element Bi constituting the main component in a proportion of more than 0 mol and equal to or less than about 0.15 mol relative to 1 mol of Bi in the main component.
The invented piezoelectric ceramic composition may mainly include, for example, a component of the formula (Sr1xe2x88x92xMx)Bi2Nb2O9, wherein M is the trivalent metallic element other than the element Bi constituting the main component, and x is more than 0 and equal to or less than about 0.3.
The invented piezoelectric ceramic composition may mainly contain a component of the formula (Sr1xe2x88x92xM2x/3)Bi2Nb2O9, wherein M is the trivalent metallic element other than the element Bi constituting the main component, and x is more than 0 and equal to or less than about 0.45.
In the invented piezoelectric ceramic composition, the trivalent metallic element other than Bi is preferably at least one selected from, for example, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
The invented piezoelectric ceramic composition may further include manganese in a proportion of more than 0% by weight and equal to or less than about 1.0% by weight calculate as MnCO3.
In another aspect, the invention provides a piezoelectric ceramic device including a piezoelectric ceramic composed of the piezoelectric ceramic composition, and electrodes formed on the piezoelectric ceramic.
The invented piezoelectric ceramic composition mainly containing a compound shown by the formula SrBi2Nb2O9 should include at least a trivalent metallic element other than the element Bi constituting the main component in a proportion of more than 0 mol and equal to or less than about 0.15 mol relative to 1 mol of Bi. If the content of the trivalent metallic element exceeds this range, the electromechanical coefficient kt is decreased and a practicable electromechanical coefficient cannot be obtained, and the temperature-dependent factor of resonant frequency is increased.
Such trivalent metallic elements other than Bi include, for example, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Sc and Y.
The present inventors also found that the electromechanical coefficient is can be improved by incorporating manganese in a proportion of about 1.0% by weight or less in terms of MnCO3 into a piezoelectric ceramic composition mainly containing SrBi2Nb2O9, in Japanese Patent Application No. 10-156648. That is also effective for the instant piezoelectric ceramic compositions, and the resulting piezoelectric ceramic compositions can yield piezoelectric ceramic devices having a high electromechanical coefficient and a low temperature-dependent factor of resonant frequency frTC.
The invented piezoelectric ceramic compositions mainly containing a component of the formula SrBi2Nb2O9 have only to have the aforementioned composition basically, and component elements may have some deviations in molar ratios.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.